The field of the invention is the production of lactams from their corresponding oximes by the Beckmann rearrangement and the present invention is particularly concerned with the production of lactams by the Beckmann rearrangement using anhydrides of sulfuric acid half esters, anhydrides of sulfonic acids or mixtures thereof as catalysts.
The preparation of lactams by oximating cycloaliphatic ketones and by the subsequent Beckmann rearrangement is known and the state of the art may be ascertained by reference to British Pat. No. 1,467,565 and US Patents 3,931,255 and 3,462,417, the disclosures of which are incorporated by reference into the present application.
The Beckmann rearrangement typically is carried out on a large industrial scale by means of concentrated sulfuric acid or oleum. In this procedure, the material being rearranged is employed in a molar amount exceeding that of the oxime. Accordingly this method suffers from the drawback that appreciable quantities of diluted sulfuric acid are processed or separated. The preparation of epsilon-caprolactam from cyclohexanonoxime is described in Ullmann's ENZYKLOPAEDIE DER TECHNISCHEN CHEMIE, Vol. 9, pp 100, 175, and the preparation of lauryllactam from cyclododecanonoxime is described by K. Weissermel and H. J. Arpe in the tome INDUSTRIELLE ORGANISCHE CHEMIE, Chemie publishers, Weinheim 1976, the disclosures of which are incorporated by reference into the present application.
It is known furthermore to rearrange alicyclic ketoximes having 9 to 14 carbon atoms in the ring with catalytic means, using merely 0.5 to 5% by weight referred to the amount of the oxime of an acid chloride such as thionyl chloride, phosphorus oxychloride, phosphorus pentachloride, benzene sulfochloride as disclosed in British Pat. No. 1,467,565.
Since these catalysts are used in substantially lesser amounts, their separation and processing inherently does not require the expenditure demanded for instance when sulfuric acid or oleum is used as the rearranging agent, as disclosed in British Pat. No. 1,467,565.
However, the method of British Pat. No. 1,467,565 entails an appreciable drawback. The lactam obtained by this procedure contains slight though not trivial amounts of chlorine, about 100 to 200 ppm. Such contaminated lactams cannot be used in the production of the corresponding polyamides. Especially as regards the further processing of the polyamides into molded bodies, the chlorinated contaminants damage the apparatus and also damage the polymers at the conventional treatment temperatures, especially because of the hydrogen chloride formed.